Efficacy and safety of an inactivated whole-virion SARS-CoV-2 vaccine (CoronaVac) in Brazilian healthcare professionals: The PROFISCOV trial

BACKGROUND: CoronaVac, an inactivated COVID-19 vaccine, underwent evaluation for its efficacy and safety during the PROFISCOV study conducted in Brazil. METHODS: Between July 21, 2020, and July 29, 2021, 13,166 participants provided informed consent, with 12,688 randomized for the trial. Participants were allocated between vaccine and placebo arms (1:1) and monitored for symptomatic COVID-19 cases, severity of disease, and adverse reactions after two doses given 14 days apart. FINDINGS: The primary efficacy analysis revealed a vaccine efficacy of 50⸱4 % (95 % confidence interval [CI], 35·3 % to 62·0 %; p = 0·0049) in preventing symptomatic COVID-19, leading to the issuance of Emergency Use Authorization for CoronaVac in January 2021. Upon completion of follow-up, vaccine efficacy was 44⸱6 % [95 % CI, 34·9 % to 52·8 %; p = 0·0023] in preventing COVID-19 and 82⸱1 % (95 % CI, 64·9 % to 90·9 %; p < 0·0001) in preventing severe COVID-19. Safety data indicated that adverse reactions were more frequent in the vaccine arm, primarily mild to moderate, with pain at the injection site and headache being the most common. INTERPRETATION: CoronaVac demonstrated moderate efficacy in preventing symptomatic COVID-19 and high efficacy against severe disease. While reactions were slightly more common in the vaccine group, they were generally mild and manageable. FUNDING: Fundação Butantan, Instituto Butantan, and São Paulo Research Foundation (FAPESP; Grants 2020/10127-1 and 2020/06409-1).